Combined manual and automatic hydraulic servomotor apparatus



Sept. 22, 1953 E. J. FENzI.

COMBINED MANUAL AND AUTOMATIC HYDRAULIC SERVOMOTOR APPARATUS Filed Mayl5, 1952 Inni-"nlm Nm? er1-leg.

Inventordwavd J. Verwzl.,

H Att b5 T Aapc.

Patented Sept. 22, 1953 COMBINED MANUAL AND AUTOMATIC HY- DRAULICSERVOMOTOR APPARATUS Edward J. Fenzl, Schenectady, N. Y., assigner toGeneral Electric Company, a corporation of New York Application May 13,1952, Serial N0. 287,656

12 Claims.

My invention relates to hydraulic servomotor apparatus, and moreparticularly to synchronizing apparatus for controlling the transfer ofservomotor control from one to another of a pair of selectable hydraulicrelay valves. The invention is particularly applicable to hydraulicservomotor systems in which one relay valve is manually controlled andthe other is automatically controlled in response to a condition, suchas in aircraft equipped with both manual and autopilot controls.

In servomotor control of aircraft where a hydraulic servomotor isutilized to move a control surface, such as a rudder, elevator oraileron, it is known to provide a hydraulic relay valve controlledmanually for power boost manual control of flight, a second hydraulicrelay valve automatically controlled by an autopilot for automaticcontrol in accordance with plane attitude, and a transfer valve forselectably connecting one or the other of the relay valves to controlthe servomotor. Since the human pilot and the autopilot exert entirelyindependent controlling influences, care must be exercised intransferring from one type of control to the other to ensure that bothcontrols, and more particularly both relay valves, are calling for thesame direction of movement or for no movement of the aircraft controlsurface at the moment of transfer. It is evident, for example, that ifat the moment of shifting the manual control is calling for right rudderand the autopilot control is calling for left rudder, a violent ruddermovement and Violent resulting change in craft attitude would resultfrom the transfer of control. It is thus necessary for smooth shiftingto effect the transfer only when the independent controlling iniluencesare synchronized to the extent that both the controls are calling forthe same direction of control surface movement or for no control surfacemovement.

It is therefore a general object of my invention to provide new andimproved means for synchronizing the transfer of control of a hydraulicservomotor from one to another of a plurality of selectable controlmembers.

It is another object of my invention to provide new and improved meansfor automatically synchronizing the transfer of hydraulic servomotorcontrol from one to another of a pair of independently operated controlvalves.

It is a more particular object of my invention to provide new andimproved means for synchronizing the transfer of hydraulic servomotorcontrol between manual to automatic in a manner 2 to prevent violentrepositioning of the controlled member. f

My invention itself will be more fully understood and its variousobjects and advantages further appreciated by referring now to thefollowing detailed specification taken in conjunction with theaccompanying drawing, the single figure of which is a schematic diagramof a hydraulic servomotor control system embodying my invention.

Referring now to the drawing, I have shown my invention by way ofillustration as applied to a combined manual and automatic hydraulicservomotor control for an aircraft control surface shown schematicallyas an aircraft rudder I. While manual control through the hydraulicsystem is provided. the rudder is provided also with direct emergencymanual control through a pair of cables 2 and a control member 3, suchdirect manual control being rendered operable in the event of failure ofthe hydraulic system,

y as will be more fully described hereinafter.

The hydraulic system comprises a hydraulic servomotor 4 having areversible piston 5 connected directly to move the rudder I. Theservomotor piston 5 is mounted in a servomotor cylinder having fluidtransfer ports 6 and 'I disposed on opposite sides of the piston.Through a pair of fluid conduits 8 and 9 the servomotor ports 6 and 'Irespectively, are connected to a pair of fluid transfer ports I0 and II,respectively, of an automatic bypass valve I2.

The bypass valve I2 comprises a duid-tight cylinder I3 having slidablymounted therein a valve spool I4 normally biased to one limit of itstravel by means of a compression spring I 5. The cylinder I3 is providedwith the fluid transfer ports I0 and II and also with an opposite pairof transfer ports I6 and I1. The valve spool I I is provided with landsso located on the spool that when the spool is in its biased positionthe fluid transfer ports I0 and II are connected together, thereby toprovide free transfer of the fluid between opposite sides of theservomotor piston 5. It is this position which the bypass valve assumesin the event that the hydraulic system fails, so that direct manualcontrol of the rudder I may be effected without resistance from theservomotor piston 5.

The bypass valve I2 is further provided at one end with a fluid inletport I8 which is connected by means of a, conduit I9 to a suitablesource of fluid under pressure, such as a pump 20. When the hydraulicsystem is in normal operation, uid supplied to the valve I2 through theport I8 actuates the valve against its bias to its opposite limit oftravel, as determined by a stop 2l, and as partially shown in dottedoutline. In this position the valve spool i4 connects the port I0 to theport i6 and the port l l to the port I, and interrupts direct connectionbetween the ports iii and il. The bypass valve l2 is provided also witha drain port 2id, through which any fluid leaking past the valve spoolI4 is returned by means of a drain conduit Zlib (shown dotted) to a sump29a. It will now benevident that the bypass valve l2 serves only as anemergency control to short-circuit opposite sides of the servomotorcylinder in the event of failure of thel hydraulic system.

The fluid transfer ports i6 and l1 of the bypass valve l2 are connected,respectively, through fluid conduits 22 and 23 to a pair of fluidtransfer ports 2li and 25S, respectively, on a transfer valve 2G. Thetransfer valve 2S serves alternatively to connect the servomotor 4 forcontrol by either one or the other of a pair of relay valves 2i, 28. Thetransfer valve 26 itself comprises a duid-tight cylinder 2e havingslidably mounted therein a valve spool 3o provided with two spaced apartoperative positions. The valve spool 3Q is biased to one of itsoperative positions by a pair of compression springs 3l, and is adaptedto be moved against its bias to its other operative position, asdetermined by a stop 32, in response to fluid under pressure suppliedthrough a fluid transfer port 33, as will be more fully describedhereinafter. The valve spool Si) is provided with a plurality of landspositioned selectably to connect the fluid transfer ports 24 and 25either with a pair of fluid transfer ports .3d and 35, respectively, orwith a pair of fluid transfer ports 36 and 3l, respectively. All theports Sli to 3l inclusive, are formed in the transfer valve cylinder 2S,as are the ports 2Q and 25. The transfer valve cylinder is provided alsoWith a drain port 33 through which fluid leaking past the valve spoolmay be returned to the sump 2M, and with a latching port 39 operable inconjunction with the uid port 33, as will be described more fullyhereinafter.

The fluid transfer ports 34 and 35 are connected through fluid conduitsi0 and Lil, respectively, to a pair of fluid transfer ports d2, 43,respectively, on the relay valve 2S, and the transfer valve ports 35 and`31 are connected through fluid conduits et and 45, respectively, to apair of fluid transfer ports 45 and 41, respectively, on the rela-yvalvel. Each relay valve is provided with a slidable valve spool Whichin a central null position seals off its associated pair of fluidtransfer ports 42, 3 or (i6, 41, and in oppositely displaced positionssupplies fluid under pressure to one or to the other of its transferports, simultaneously connecting its other transfer port to the drainconduit 2Gb. The relay valve 2l is manually controlled, and the relayvalve 28 is automatically controlled through a suitable autopilotsystem.

Referring now more particularly to the relay valve 2l, this valvecomprises a fluid-tight cylinder 118 within which is slidably mounted amovable valve spool 139. The valve spool 49 is manually movable by meansof a valve stem G. The valve cylinder li is provided with the fluidtransfer ports llS and 'i1 as described, and is provided also with afluid inlet port 5i and a pair of fluid drain ports 52, 53 adapted to beconnected through the drain conduit 2% to the sump 20a. Opposite ends ofthe valve cylinder beyond the passageways 5ta and 51a,

ends of the valve spool if are connected to the drain ports '52 and 53by passageways 52a, 53a, respectively, formed in the valve cylinder. Inthe central null position of the valve spool lit, this spool seals offthe inlet port 5l and the fluid transfer ports It and lli as Well as thedrain ports 52 and 53. When the valve spool 49 is moved to the left, asshown in the drawing, fluid under pressure is supplied from the inletport 5l to the transfer port d5, and the transfer port 4? is connectedto the drain port 52. When the valve spool 49 is moved to the right ofits central null position, as shown in the drawing, fluid under pressureis supplied from the inlet port 5i to the fluid transfer port Il? andthe fluid transfer port i5 is connected to the drain port 53.

rIhe relay valve 28 is generally similar to the relay valve 21 exceptthat it is provided in addition with certain control ports through whichmovement of the valve spool may be controlled by suitable applicationand release of fluid pressure at opposite ends of the valve spool.v Moreparticularly, the relay valve 23 comprises a fluidtight valve cylinder54 within which is slidably mounted a valve spool 55 movable in oppositedirections from a central null position in which it is shown in thedrawing. The valve cylinder 54 is provided with the fluid transfer ports62, 43 as described, and with a pair of fluid inlet ports 5S, 5i, a pairof control ports 53, 5S and a drain port 69. The drain port Sii isconnected through the drain conduit 2th to the fluid sump Zlio. Thefluid inlet ports 5S and 5l are connected through a fluid supply conduit6l to the pump 2li. By respectively, the fluid supply ports 55 and Elare connected to opposite ends of the valve cylinder beyond the ends ofthe valve spool 55, these passageways being positioned to be covered bythe terminal lands on the valve spool in the opposite limiting positionsof the spool. It will now be. understood that Whenthe valve spool 55 ofthe relay valve 28 is in its central null position as shown, the fluidinlet conduits 5E and V5T are sealed, as are also the fluid transferconduits A2, 43 and the drain conduit 6d. Through the passagevfays 56aand 57a uid under pressure is supplied from the inlet conduits 52S and57, respectively, to opposite ends of the valve spool so that the valvespool is under opposing but balanced pressures.

The control ports 58 and 59 of the relay valve 28 are connected throughconduits G2 and respectively, to a pair of fluid transfer ports Ed and65, respectively, of a reversible solenoid control valve '65. Thesolenoid valve 65 comprises a fluid-tight cylinder 81 within which isslidably mounted a valve spool 68 movable from a central null positionshown in the drawing to op.- posite control positions in which eitherthe port 54 or the port S5 is connected through the valve with a drainport Eil. The valve spool 68 is normally centered in a null position inwhich the ports 64, 65 and "59 are sealed oi, and is maintained in thisposition by a pair of opposing centering springs (not shown). The valvespool 68 is connected to be moved in opposite directions by means of apair of solenoids 'iii and 'H forming part of an automatic pilot controlsystem. A suitable autopilot control system including such an oppositelyacting solenoid valve is shown in Patent No. 2,464,629 issued to Youngand assigned to the same assignee as the present application, whereinthe solenoids 2T and 23 (Fig. 1b) correspond to the solenoids 1li and 1lof the instant application.

For the purpose of actuating the transfer valve V-26 between its twooperative positions and thereby selectably connecting either the relayvalve 21 Vor'the relay valve 28 to control the servomotor port 33 of thetransfer valve 26 either to a source of fluid under pressure or to thesump 29a, both such connections being made through the balanced matchingvalve 13. The matching valve 13 is normally centered, and when socentered it completes connection of the selector valve 12 with thetransfer valve port 33. The matching valve 13 is differentiallyresponsive to fluid pres- Asure at two selected .relay valve transferports which are adapted for alternative connection to A the sameservomotor port, and pressures of. un-

`(to the right as shown in the drawing) to its other position by meansof a solenoid 16. The valve cylinder is provided with a fluid inlet port11, a pair of fluid drain ports 18, 19, and a fluid transfer port Bil.In the normal position of the selector valve spool 15 the fluid inletport 11 is sealed off by the valve spool and the fluid drain port 19 isconnected through passageways 8| and 82 in the valve cylinder and thevalve spool, re-

spectively, to the fluid transfer port 30. The selector valve transferport 89 is connected by a fluid conduit 93 to the transfer valvelatching port 39 and, as will be later described, by a conduit 84 to auid transfer port on the matching valve 13. A manually operable switch1E@ is shown for `energizing the selector valve solenoid 15.

Referring now more particularly to the matching valve 13, this valvecomprises a fluid-tight cylinder 95 within which is slidably mounted avalve spool 35 normally centered in the position shown in the drawing bymeans of a pair of opposing compression springs 31. Opposite ends of thematching valve cylinder 85 are connected through conduits 38 and 89 tothe transfer ports 41 and 43, respectively, on the relayv valves 21 and28, respectively. It maybe noted here, as will be more evidenthereinafter, that the relay valve ports 41 and 43 are adapted to bealternatively connected through the transfer valve 26 and the bypassvalve l2 to the same servomotor port 1. These relay valve ports 41 and43 are shown, and this groove 93 is connected by an internal passageway94 in the valve spool with a portion of the spool which is normally incommunication with the valve port 90. It will thus be observed that whenthe matching valve spool 8B is in its normal centered position its ports90 and 9! are in free communication with each other through the groove93 and the passageway 94, but when the spool is displaced from itscenter position in either direction, the port 9| is closed off.

In view of the foregoing detailed description of thestructure andinterconnection of my new and .improved apparatus, its mode ofloperation will now` bereadily understood from the following briefdescription..

`'lihe apparatus is shown in the drawing in condition for manual powerboost control of thev rudder I through the relay Valve 21. In thisconnection it will be observed that the selector valve solenoid 16 is(ie-energized and the selector valve is in the position shown in thedrawing. If it is further assumed that neither the autopilot nor theoperator is at the moment demanding any movement of the rudder l, bothrelay valves 21 and 28 are in the null positions shown, so that thematching valve 13 is centered as shown in the drawing. With the matchingvalve centered and the selector valve 12 in its biased position shown,the transfer valve port 39 is connected to the sump through the conduit83, the selector valve port 89 and the selector valve passageways 32 and3i, and the transfer valve, port 33 is connected to the sump through theconduit 92, the matching valve port 9i, the matching valve passageways93 and 94, the matching valve port 90, the conduit 84, the selectorvalve port 89 and the selector valve passageways 82 and Si. Thus nofluid pressure is supplied to the left end of the transfer valve 26 andthis valve is in its biased position shown in solid lines on thedrawing. In this position of the transfer valve its ports 34 and 35 aresealed off, thereby to disable the relay valve 28, and the transfervalve ports 36 and 31 are connected respectively to the ports 24 and 25.The transfer valve 26 is thus positioned to connect the ports 43 and 41of the manual relay valve 21 to the servomotor ports 5 and 1,respectively.

So long as the relay valve 21 remains in its null mid-position shown, nomovement of the servomotor piston 5 is effected. If, however, the

. relay valve spool 49 is moved to the left, as

therefore transfer ports of similar function, in Y 9| which is connectedby a fluid conduit 92 to the port 33 of the transfer valve 25. Thematching valve spool 86 is circumferentially grooved at 93 at a pointwhich registers with the port 9| when the spool is initsnormalhmidposition 1 shown. in the drawing, the relay valve ports 46`and.5l are interconnected, thereby to apply fluid pressure through theconduit 44, the transfer valve 26, the conduit 22, the bypass valve I2and the conduit 8 to the servomotor port 6. At the same time, the port41 of the relay valve 21 is connected to the drain port 52, so that theservomotor port 1 is connected to the sump through the conduit 9, thebypass valve l2, the conduit 23, the transfer valve 25, the conduit 45,and the ports 41 and 52 of relay valve 21. Thus, the servomotor piston 5will move to the right as shown in the drawing. It will be evident tothose skilled in the art that movement of the relay valve spool 49 tothe right of its midposition effects an opposite movement of theservomotor piston 5 in an entirely similar manner. In this condition ofthe apparatus movement of the relay valve spool 55 of the autopilotcontrolled relay valve 28 has no effect upon the servomotor 4 becausethe fluid conduits 4l! and 4l from the fautomatic or `autopilot.operation of the apparatus, the manual switch 85 is closed, thereby .to

:energize the selector 'valve solenoid l landrnove the selector valve.lEto the rightfas shown inthe drawing. Such movement .of the selectorvvalve 'connects its fluid inlet p ort 'il with .the fluid transfer portSil, thus supplying fiuidunderppi'essure to the latcning port 3S of thetransiervalve l261and also vto the port til of the'matchingvalve "113.

lfupon such actuation of theselectorvalve 552 the matching valvelsziscenteredas shownin the drawings, duid under pressure .is .suppliedfrom the port @5l of the matching valve through lpassageway '94 `to itsport Si, and through the yconduit 92 to the port 'd3 4of the transfervalve 2 6.

Fluid under pressure at the 'transfer .valve port 33 'forces Vthe valvespool te of the transfer valve to the right against :itsbias to thedottedposition shown inthe drawing. When the transfervalve -spool 3Garrives in its right-hand position, itis maintained in that position, orlatched, hy direct supply of fluid under pressure from the selector`valve port @il through the conduit 83 andthe transfer valve latching'port 3S. It is evident that huid thus supplied through the transfer-valve latching port 39 is controlled by the selector valve l2 only, andis then independentof displacement of the matching valve i3.

The foregoing movement of the transfer Valve spool Si?, however, dependsupon free interconnection between the ports 9d and @i of the matchingvalve "53. Such interconnection only exists if the matching valve spool86 is in its normal centered position. 'The matching lvalve spool 325will be in this centeredposition so long Yas the fluid supplied toopposite ends of the valve cylinder 85 from the relay valve transferports '43 and all (on the relayvalves'ZS and'lyrespestively) is underpressure of like kind. "That is,

:if the'fluid at both relay valveports A3 and fil' Vis under positivepressure, or if the 'fluid Vat both these ports is under Zero pressure,`the .matching Valve will remain balanced. If, however, huid at one ofthe relay valve ports 43 or lil is under positive pressure, while theother is at zero (i. e. sump) pressure, the matching valve will .bedisplacedto the right or to theleft depending'upon which o'f the relayvalve ports is under'positive pressure. 'Such displacement of thematching valve T3 vfrom its normal centered position interrupts theconnection betweenthe matching lvalve ports 96 and Si andprevents'supply of iiuid under pressure to the Vtransfer valve port 33,even though the selector valve i2 has 'been moved'to 'a `position tosupply such huid. This 'means of course that "the matching valve 13 willVbe Vdisplaced lfrom its normal centered position-when- ;ever vthemanual relay valve 27 vis calling for -a servomotor action (or inaction)different from that being called forby the autopilot relay valve Morespecifically, if both the manual relay valve `2'!! and theautopilotrelay valve 28 are in theirnull midpositions shown, so thatneither is `calling for any movement of the servomotor pisthe matchingvalve T53 will remain balanced. In

:any of y.these circumstances, then, the Vtrar-1sfer Vvalve spool .3.9will .he moved limmediately .upon

A.movenfient of the yselector valve l2.

lf, however, the manual relay valve .-27 .is .calliingior movement ofthe servomotor piston v5 to ithe left (positive pressure at the relayvalve port 61), Vwhile-.the autopilot relay valve y2t is calling rforeservomotor movement to the -right (sump pressure at itherelay valveport 43) the Amatching valve 1:3 rwill -be displaced to ,the right and:fluid runder pressure will not be supplied to the transfer valve portf3-3 until -a `balanced condition Eis restored. The opposite 4conditionof Vunlcavlance V`will beevident to ,those skilled inthe art.

Thus/it 'will hessen that-with mynewandiimproved.apparatusymovement `ofthe transfer .valve :.26 .from cone operative position pto another :totransfer .control .of the .servonintor `Il from the :manualirelayvalveZi'totheautopilot relay valve :28.cannut 4loe-carried out,.even,though ,calledfforhy the selector vvalve '52,'untila likeconditionpfthe lrelay -valves is indicated Icyautomatic v'balancing of:t-hematching 'valve l5. This precludesxviolent repositioningofvthe-rudder I which mightotherwise result from transferring at a momentwhen lone relay valve was calling .for one direction of vrudder movementwhile the other was calling 'for the other direction of rudder movement.

It might appear from the above description of Vthe operation that therecould be circumstances 'in which a shift of the matching Valve 13 fromthe centered position which is shown is called for by a difference inthe positions of relay valves 21 and 23, but in which no suchdisplacement is achieved because one of the end chambers of the matchingvalve casing is eifectively sealed up to prevent the required change involume for 'matching valve movement. This apparent difficulty wouldoccur whenever the relay valve 2! or 123, to which control of the servopiston 5 is to be shifted, is in the neutral position shown in thedrawing. For instance, with the transfer valve :spool 30 in the positionshown in solid lines, so 'thatithepiston 5 is under the control of themanually operated relay valve'2'l, a shift of transfer valve spool 3i]would cause a shift of control to the automatically actuated relayvalve23. Howfever, the right-hand end chamber of matching valve casing85 apparently cannot change in volume since the only outlet conduit 8Bis apparently closed at transfer .valveport 35 and at con- `duitdl andport 43 of relay ,valve 28 by meanslof the closure of relay valvepcrts55 andl. It will be understood, however, that although the abovedescription'has repeatedly referred to the operation of Wthe-valvespools as .seaiingoff the various 'associated ports, it is animpossibility from a practical standpoint .to 4provide movableVhydraulic valve spools ofthe type disclosed vin this -system which arecompletely leakproof. It will Vice understood therefore that thecomhinedleakages of the valve spool 8E adjacent to the righthand end chamber ofmatching valve casing 85 thespool 3B in the vicinityvof port 3 5 oftransfer Valve. 26,.and the spool 55 in the vicinity of vports 53 and,Bil of relay valve 28, are sufficient to permit displacement ofthematching valve spool by the very small amount which is necessary toshift the circumferentialrgroove 93 out of alignment with the Aport 9iwhen reguired torprevent operation of the transfer valve 2,6 asdescribed above.

It will now readily he appreciated by those skilled in the artthatreverse transferis carried putin-an Aentirely similar and automaticallycontrolled manner. Specifically,'if it is desired to retransfer fromcontrol by the autopilot relay valve 28 to control by the manual relayvalve 2l, the selector valve solenoid 'I6 is de-energized and theselector valve 12 permitted to assume its biased position shown in thedrawing. If at the moment the selector valve returns to this position,the matching valve i3 is balanced as shown, the transfer valve port 33is connected to the sump through the conduit 92, the matching valveports 9| and 9c, the conduit 8d and the selector valve ports 8G and 19.The transfer valve latching port 39 is also directly connected to thesump through the selector valve ports 80 and 79. The transfer valvespool 3U then moves under the influence of its biasing springs 3| to theposition shown in solid lines in the drawing. If, however, at the momentthat the selector valve spool 15 is returned to the position shown, thematching valve spool 86 is displaced due to unlike pressure conditionsat the relay valve ports i3 and 47, the transfer valve port 33 is sealedoif from the sump by sealing oif of the matching valve port 9i.Retransfer, therefore, cannot take place until the matching valve 13 isrestored to its balanced condition. As soon as such restoration is made,however, transfer automatically takes place.

It will of course be understood by those skilled in the art that, when Irefer in the foregoing to a hydraulic system or apparatus I refer to onewhich operates in response to the supply of any suitable liquid fluid,such as oil, under pressure.

While I have described only a preferred embodiment of my invention byway of illustration, many modifications will occur to those skilled inthe art, and I therefore wish to have it understood that I intend in theappended claims to cover all such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of uid transfer ports disposed on oppositesides of said piston, a pair of relay valves each having a pair of iiuidtransfer ports, means including a transfer valve for alternativelyconnecting either said pair of relay valve ports to said servomotorports thereby selectively to connect one or the other of said relayvalves to control said servomotor, and means differentially responsiveto iiuid pressure at two of said relay valve ports adapted foralternative connection to' the same one of said servo-` motor ports forcontrolling said transfer valve.

2. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of fluid transfer ports disposed onopposite sides of said piston, a pair of relay valves each having a pairof iiuid transfer ports, means including a transfer valve having spacedapart operative positions for alternatively connecting either said pairof relay valve ports to said servomotor ports thereby selectively toconnect one or the other of said relay valves to control saidservomotor, means for biasing said transfer valve to one said operativeposition, and means Vdifferentially responsive to fluid pressure at tworelay valve transfer ports of like function for supplying fluid underpressure to actuate said transfer valve to the other-said operativeposition. Y

i 3. In a hydraulic apparatus for actuating a movable member, ahydraulic servomotor having a reversible piston adapted to be connectedto move said member and having a pair of fluid transfer ports disposedon opposite sides of said piston, a pair of relay valves each having apair of fluid transfer ports, means including a transfer valve havingspacedy apart operative positions for alternatively connecting eithersaid pair of relay valve ports to said servomotor ports therebyselectively to connect one or the other of said relay valves to controlsaid servomotor, means for biasing said transfer valve to one saidoperative position, means differentially responsive tofluid pressure attwo of said relay valve ports adapted for alternative connection to thesameone of said servomotor ports for moving said transfer valve to theother said operative position when pressures of lik-e kind exist at saidtwo relay valve ports, and means independent of said differentialresponsive means for maintaining said transfer valve in said otheroperative position.

4. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of iiuid transfer ports disposed onopposite sides of said piston, a pair of relay valves each having a pairof iiuid transfer ports, means including a transfer Valve having spacedapart operative positions for alternatively connecting either said pairof relay valve ports to said servomotor ports thereby selectively toconnect one or the other of said relay valves to control saidservomotor, a selector valve, means connecting said selector valve tosupply fluid under pressure to control movement of said transfer valvebetween said operative positions, and means differentially responsive tofluid pressure at two relay valve transfer ports of like function forcontrolling said connecting means.

5. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of iiuid transfer ports disposed onopposite sides of said piston, a pair of relay valves each having a pairof fluid transfer ports, means including a transfer valve having spacedapart operative positions for alternatively connecting said pairs ofrelay valve ports to said pair of servomotor ports, se lector means forcontrolling movement of said transfer valve between said positions,means connecting said selector means to said transfer valve, and meansdifferentially responsive to fluid pressure at two relay valve transferports adapted for connection to the same one of said servomotor portsfor disabling vsaid connecting means when fluid pressures of unlike kindexist at said two relay valve ports.

6. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of iiuid tranfer ports disposed onopposite sides of said piston, a pair of relay valves each having a pairof fluid transfer ports, means including a transfer valve having spacedapart operative positions for alternatively connecting said pairs ofrelay valve ports to said pair of servomotor ports, means biasing saidtransfer valve to vone said operative position, a selector valve, meansincluding a balanced -valve connecting said selector valve to supplyiiuid under pressure to actuate said transfer valve against its bias tothe othersaid operative position, said balanced valve beingdifferentially responsive to fluid pressure at two relay valvel ports oflike function to control saidv supply of fluid to said transferl valve,and means controlled by said selector valve and said transfer valveindependently of said balanced valve for supplying fluid under pressureto maintain said transfer valve in said other operative position.

7. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of fluid transfer ports disposed onopposite sides of said piston, a pair of relay valves each having a pairof fluid transfer ports, meansrincluding al transfer valve having spacedapart operative positions, said transfer valve in oneposition'connecting the transfer ports of one relay valve tothe transferports of said servomotor and in the other position connecting thetransfer ports of the other said relay valve to the transfer ports ofsaid servomotor, each said relay valve when connected being movabletosupply uid under pressure to one or the other of its transfer portsand-through said transfer valve to one or the other of said supply fluidtoand exhaust fluidfrom said transfer valve to control movement of .saidtransfer valve between said operative positions, said connecting meansincludinga matching valve operable when displaced'from a normalcentered-posi tion to disable said connecting means, means Y biasingsaid matching valve tosaid centered posi tion, means differentiallyresponsive to` fluid pressure at transfer ports of like function on theconnected and unconnected relay valves to displace said matching valvefrom said centered position, and means controlled by said selector valveand said transfer valve independently of said matching valve forsupplying fluid under pressure to maintain saidtransfer valve inposition against its bias.

8. In a hydraulic apparatus for actuating a movable member, a` hydraulicservomotor having a reversible piston adapted to be connected to movesaid member and having a pair of fluid transfer ports disposed onopposite sides of said piston, a pair of relay valves each havingal uidinlet port and a pair of fluid transfer ports, said relay valves eachhaving. av null position and opposite operative positions in which itsinlet port is alternatively connected to one. orthe other of itstransfer ports, means supplying uid under pressure to said inlet ports,manuallyr operable means for actuating one said relay valve, meansautomatically responsive to a controlling condi-v tion for actuating theother said' relay valve,` means including a uid transfer valve` havingtwo spaced apart operative positions for-alterf natively connecting saidpairs` of relayV valvetransfer ports to said servomotor ports, meansbiasing said transfer valve to one of its operative positions, selectormeans for supplying-fluid under pressure to movesaidtransfer valveagainst its bias and exhausting fluid from said transfer valve forreverse movement, aV matching valve dilfe;- entially responsiveto fluidpressure at-connected and unconnected relay valve transfer ports of likefunction to disable said selector means whenever fluid pressures ofunlike kinds exist at said relay valve ports of like function, and meanscontrolled by said selector` means independentlyy of said matching valvefor supplying fluid' under pressure to maintain: said transfer valve inposition against its bias.

9. In a hydraulic apparatus for actuating a movable member, a hydraulicservomotor having a reversible piston adapted to` be connected tomovesaid member and having a pair of fluidr transfer ports disposed onopposite sides of" said piston, a pair of relay valves each` having apair of fluid transfer ports, means including a1 transfer valve havingtwo spaced apart operative posi',- tions for alternatively connectingeither said pair of relay valve ports to said servomoton ports therebyselectively to connect one or the other of said relay valves to controlsaidV servomotor,

means for biasing said transfer valve to one said' operative position,selector means forl alterna,- tively supplying fluid underk pressure tosaid transfer valve to movesaid valve aganstits bias, and exhaustingfluidfrom said valve for oppositev movement, and means differentiallyresponsive to fluid pressure at two relay valve transfer ports4 adaptedto be connected to the same servomotor port for disabling saidselector'means whenever iluid pressures of unlike kind exist atsaidftwo` relay valve ports.

10. In a control system for a dirigible` craft having a control surface,a hydraulic servomotor having a reversible piston adapted to beconnected to move said-surfacefandhaving a pa-irpof fluid transfer portsdisposed on opposite sides of said piston, a pair of vrelay valves eachhavingr a pair of fluid transfer ports, manually' operable means foractuating one said relay valve, means responsive to a component of craftattitude for automatically actuating the other Vsaid relay valve,`

each said relayv valve when actuated supplying fluid under pressure atone or the other of its, transfer ports, means including a transfervalvel for alternatively connectingA either said pair of relay valveports to said servomotor ports thereby selectively to connect one or theother of said relay valves to control said servomotor, and meansdifferentially responsive to fluid pressure at two of saidy relay valveports adapted for alternative connection to the same one of saidservomotor ports for controlling said transfer valve.

1l. In a control system for a dirigible craft having a control surface,a hydraulic servomotor having a reversible piston adapted to beconnected to move said surface and having a pair. of fluid transferports disposed on opposite sides of said piston, a pair of relay valveseach having a pair of fluid transfer ports, manuallyy operable means foractuating one said relay valvemeans responsive to a component of craftattitude for automatically actuating the other said relay valve. eachsaid relay valve-` when actuated supplying fluid under pressure at oneor the other ofv its transfer ports, means including a transfer valvehaving two spaced apart operative positions foralternatively connectingeither said pair ofrelay valve ports to said servomotor ports therebyselectively to connect one or the other of' said relay'valves to controlsaid servomotor, manually operable selector means for supplying fluidunderk pressure to and exhausting fluid from saidtrans-n fer valve tocontrol movement of said valve-between said operative positions, andmeansdif ferentially responsive to fluid pressure atv two relay valvetransfer ports of like function for disabling said selector meanswhenever fluid pressures of unlike kind exist at said two relay valve.A

ports.

l2;Y In a control .system for a dirigible craft.

' having a control surface, a hydraulic servomotor 13 having areversible piston adapted to be connected to move said surface andhaving a pair of fluid transfer ports disposed on opposite sides of saidpiston, a pair of relay valves each having a pair of uid transfer ports,manually operable means for actuating one said relay valve, meansresponsive to a component of craft attitude for automatically actuatingthe other said relay valve, each said relay valve having a nullmidposition and when actuated away from said null inidpositon supplyingfluid under pressure at one or the other of its transfer ports, meansincluding a transfer valve having two spaced apart operative positionsfor alternatively connecting either' said pair of relay valve ports tosaid servornotor ports thereby selectively to connect one or the otherof said relay valves to control said servo-' motor, means biasing saidtransfer valve to one of said operative positions, manually operableselector means for supplying uid under pres- 2 sure to and exhaustingiiuid from said transfer valve to move said valve against its bias andtc permit reverse movement respectively, means differentially responsiveto fluid pressure at two relay valve ports adapted for alternativeconnection to the same one of said servomotor ports for rendering saidselector means operable to supply and exhaust uid only when pressures oflike kind exist at said two relay valve ports, and means controlleddirectly by said selector means independently of said diiferentiallyresponsive means for supplying fluid under pressure to maintain saidtransfer valve in position against its bias.

EDWARD J. FENZL.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,325,108 Carlson July 27, 1943 2,611,560 Harcum Sept. 23,1952

